Polyurethane polymer or oligomer having carbamate groups, method for its preparation, and coating composition

ABSTRACT

Polyurethane polymers having pendant carbamate groups are disclosed. The polymers are prepared by: 
     (a) reacting a mixture comprising a polyol having at least one pendant carbamate group and a polyisocyanate to form a polyurethane having pendant carbamate groups, and 
     (b) optionally, capping the polyurethane from (b) with an active hydrogen-containing capping agent.

This is a divisional of application Ser. No. 08/361,344 filed on Dec.21, 1994, now abandoned.

FIELD OF THE INVENTION

This invention relates to polymers, and in particular to curable coatingcompositions that contain a polyurethane having pendant carbonate group.

BACKGROUND OF THE INVENTION

Polymers and oligomers having carbamate functional groups have been usedin a variety of curable compositions. Carbamate-functional acrylicpolymers are described, for example, in U.S. Pat. No. 5,356,669 and WO94/10211. These can be prepared by addition polymerization ofcarbamate-functional acrylic monomers or by transcarbamylation of ahydroxy functional acrylic with an alkyl carbamate. Carbamate-functionalpolyesters, prepared by transcarbamylation of a hydroxy-functionalpolyester, are described in JP 51/4124.

Polyurethane resins are also widely used in curable compositions such ascoating compositions. These resins offer many beneficial properties,such as good durability, good dispersibility in aqueous systems throughincorporation of appropriate tonic or nontonic stabilizing groups,impact resistance, good adhesion, and other physical properties such asstress release. One area of concern with polyurethane resins for curablecompositions has been the incorporation into the resin of sufficientlevels of functional groups to achieve the desired cure performance.Hydroxyl groups are commonly used as functional groups in curablecompositions, but polyurethane resins with pendant hydroxyl groups aredifficult to prepare since any pendant hydroxyl groups would be consumedby reaction with isocyanate during formation of the polyurethane.Hydroxyl functional groups are usually incorporated onto polyurethaneresins by the use of polyol capping agents like trimethylol propaneresulting in terminal OH groups, but no pendant OH groups. Such resinsprovide only limited crosslink density upon cure. The crosslink densitymay be increased somewhat by using branched polyurethanes, which areprepared by the incorporation of trifunctional or higher functionalpolyols in the polyurethane reaction mixture. However, the degree ofbranching is often limited due to gelation. Low crosslink density mustoften be compensated for by using higher molecular weight resins thatmore closely resemble thermoplastic compositions than thermosetcompositions.

Carbamate-functional polyurethanes are described in U.S. Pat. No.5,373,069. This reference describes the preparation of polyurethaneshaving carbamate terminal groups by a variety of schemes, such ascapping an isocyanate-terminated polyurethane with a hydroxyalkylcarbamate. The reference also discloses the preparation of polyurethaneshaving pendant carbamate groups by first preparing a polyurethane havingpendant acid groups by known techniques, and then transesterifying theacid groups with a hydroxyalkyl carbamate. This approach involves asynthetic route that can be difficult. Moreover, it results inconsumption of acid groups on the polyurethane, which are not thenavailable for aqueous stabilization of the resin.

Accordingly, the present invention is directed toward a new method ofpreparing polyurethane polymers or oligomers having pendant carbamategroups. It is also directed to a polyurethane resin having both pendantcarbamate groups and acid groups.

SUMMARY OF THE INVENTION

According to the present invention, a method of preparing a polyurethanepolymer or oligomer is provided comprising:

(a) reacting a mixture comprising a polyol having at least one pendantcarbamate group and a polyisocyanate to form a polyurethane havingpendant carbamate groups, and

(b) optionally, capping the polyurethane from (b) with an activehydrogen-containing capping agent.

Another embodiment of the present invention is directed to apolyurethane polymer or oligomer having both acid groups and carbamategroups.

In another embodiment of the invention, there are provided curablecoating compositions comprising the above-described carbamate-functionalpolyurethanes and a curing agent that is reactive with carbamate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The polyol having at least one carbamate group appended thereto can beprepared in a variety of ways. One method is to react a compound havinga plurality of cyclic carbonate groups with ammonia, ammonium hydroxide,or a primary amine to ring open the cyclic carbonate groups. Thisring-opening reaction converts each cyclic carbonate ring to a hydroxylgroup and a pendant carbamate group.

The compound having a plurality of cyclic carbonate groups can beprepared in several ways. One technique is to react a polyisocyanate ora polyanhydride with a hydroxyalkyl cyclic carbonate. Hydroxyalkylcyclic carbonates can be prepared by a number of approaches. Certainhydroxyalkyl cyclic carbonates like 3-hydroxypropyl carbonate (i.e.,glycerin carbonate) are commercially available. Cyclic carbonatecompounds can be synthesized by any of several different approaches. Oneapproach involves reacting an epoxy group-containing compound with CO₂,preferably under pressure with a catalyst. Useful catalysts include anythat activate an oxirane ring, such as tertiary amine quaternay salts(e.g., tetramethyl ammonium bromide), tin and/or phosphorous complexsalts (e.g., (CH₃)₃ SNI, (CH₃)₄ PI). Epoxides can also be reacted withβ-butyrolactone in the presence of such catalysts. In another approach,a glycol like glycerins is reacted at temperatures of at least 80° C.(usually under reflux) with diethyl carbonate in the presence of acatalyst (e.g., potassium carbonate) to form a hydroxyalkyl carbonate.Alternatively, a functional compound containing a ketal of a 1,2-diolhaving the structure: ##STR1## can be ring-opened with water attemperatures of at least 60° C., preferably with a trace amount of acid,to form a 1,2-glycol, which is then further reacted with diethylcarbonate to form the cyclic carbonate.

Cyclic carbonates typically have 5-6-membered rings, as is known in theart. Five-membered rings are preferred, due to their ease of synthesisand greater degree of commercial availability. Preferred hydroxyalkylcyclic carbonates used in the practice can be represented by theformula: ##STR2## where R is a hydroxyalkyl group of 1-18 carbon atoms,preferably 1-6 carbon atoms, and more preferably 1-3 carbon atoms, and nis 1 or 2, which may be substituted by one or more other substituentssuch as blocked amines or unsaturated groups. More preferably, R is--C_(m) H_(2m) OH where the hydroxyl may be primary or secondary and mis 1 to 8, and even more preferably, R is --(CH₂)_(p) --OH where thehydroxyl is primary and p is 1 to 2.

The organic polyisocyanate that can be reacted with the hydroxyalkylcyclic carbonate is essentially any polyisocyanate and is preferably adiisocyanate, e.g., hydrocarbon diisocyanates or substituted hydrocarbondiisocyanates. Many such organic diisocyanates are known in the art,including p-phenylene diisocyanate, biphenyl 4,4'-diisocyanate, toluenediisocyanate, 3,3'-dimethyl-4,4 biphenylene diisocyanate,1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate,2,2,4-trimethylhexane-1,6 diisocyanate, methylene bis (phenylisocyanate), 1,5 naphthalene diisocyanate, bis (isocyanatoethylfumarate), isophorone diisocyanate (IPDI), tetramethylxylenediisocyanate, and methylene-bis-(4 cyclohexylisocyanate). There can alsobe employed isocyanate-terminated adducts of diols, such as ethyleneglycol, or 1,4-butylene glycol, etc. These are formed by reacting morethan one mole of a diisocyanate, such as those mentioned, with one moleof a diol to form a longer chain diisocyanate. Alternatively, the diolcan be added along with the diisocyanate.

While diisocyanates are preferred, other multi-functional isocyanatesmay be utilized. Examples are 1,2,4-benzene triisocyanate andpolymethylene polyphenyl isocyanate.

The polyisocyanate and hydroxyalkyl cyclic carbonate reaction can beperformed under conditions known in the art for the reaction of alcoholsand isocyanates.

Polyanhydrides that can be reacted with a hydroxyalkyl cyclic carbonateinclude any of a number of compounds well-known in the art, e.g.,hexahydrophthalic anhydride, methyl hexahydrophthalic anhydride, maleicarthydride, glutamic anhydride, 1,2,4,5-bis-anhydride cyclohexane. Theconditions for this reaction are generally at least 80° C., preferably98°-120° C., in the presence of a tin metal catalyst.

Compounds having a plurality of cyclic carbonate groups can also bereadily prepared by reaction of a polyepoxide with carbon dioxide toconvert the epoxy groups to cyclic carbonate groups. Polyepoxides arewell-known in the art. Useful polyepoxides include the trimethylolpropane that has been epoxidized by reaction with an epihalohydrin, andalso epoxy-novolacs. Oligomeric or polymeric polyepoxides, such asacrylic polymers or oligomers containing glycidyl methacrylate orepoxy-terminated polyglycidyl ethers, can also be used. Otherpolyepoxides, e.g., epoxy-novolacs, may also be used. As with otherpolyepoxides, epoxy-novolacs can be reacted with carbon dioxide to formthe cyclic carbonate compound.

Although linear polyurethanes will be based primarily on compoundshaving two functional groups for the urethane reaction, cycliccarbonates with a functionality higher than 3 are also contemplated toprovide branched polyurethanes. For example, the isocyanate groups on adiisocyanate such as isophorone diisocyanate may be adducted with apolyol such as trimethylol propane to produce a tetrafunctional alcohol,which can be epoxidized with an epihalohydrin to produce atetrafunctional polyepoxide, which is in turn reacted with carbondioxide to form a tetrafunctional cyclic carbonate. Otherhigher-functionality polyepoxides, e.g.,tetrakis(4-glycidyloxyphenyl)ethane, may also be reacted with CO₂ toform poly-cyclic carbonates.

The compound having a plurality of cyclic carbonate groups is reactedwith ammonia, ammonium hydroxide, or a primary amine. This reaction isperformed under mild conditions (e.g., 0°-60° C. in water, methanol, orother known solvents. Reaction with ammonia or ammonium hydroxide yieldsa primary carbamate, and is preferred. Reaction with a primary amineyields a secondary (N-substituted) carbamate. The ring-opening reactionof ammonia, ammonium hydroxide, or a primary amine with the cycliccarbonate group yields a carbamate group as described above and also aprimary or secondary hydroxyl group, which takes part in thepolyurethane-forming reaction in the next step of the invention. Thisreaction product thus comprises pendant carbamate groups, and terminalhydroxyl groups.

Another technique to prepare a polyol having at least one pendantcarbamate group appended thereto is to react a hydroxyalkyl cycliccarbonate with ammonia, ammonium hydroxide, or a primary amine. Thisreaction is performed as described above with respect to the ringopening of the compound having plurality of cyclic carbonate groups. Theresulting compound has two hydroxyl groups and one pendant carbamategroup.

The pendant carbamate groups on the polyurethane of the presentinvention can be primary or secondary groups. Primary carbamate groupscan be represented by the formula: ##STR3## and secondary carbamategroups can be represented by the formula: ##STR4## where R issubstituted or unsubstituted alkyl of 1-8 carbon atoms, preferably 1-4carbon atoms, and more preferably 1 carbon atom, or cycloaliphatic. Itis to be understood that the terms alkyl and cycloalkyl are to includesubstituted alkyl and cycloalkyl, such as halogen-substituted alkyl orcycloalkyl or unsaturated group-substituted alkyl. Substituents thatwill have an adverse impact on the properties of the cured material,however, are to be avoided. Primary carbamates are formed in theabove-described ring-opening reactions of cyclic carbonates through theuse of ammonia or ammonium hydroxide as the ring-opening reactant.

In step (b) of the present invention, a mixture comprising the reactionproduct of step (a) and a polyisocyanate is reacted to form apolyurethane. This mixture may also comprise additional components usedin the preparation of polyurethanes, such as other monomeric, polyols,fatty polyols, or oligomeric or polymeric polyols, additionalpolyisocyanates, polyisocyanate prepolymers, polyamines, amino alcohols,triisocyanurates, and the like. The above components may be reacted inthe same pot, or may be reacted sequentially, depending upon the desiredresults. Sequential reaction produces resins which are more ordered instructure. The reaction product of step (a) and the otherabove-described compounds with active hydrogen groups may serve as chainextenders to build up the polyurethane backbone through reaction ofactive hydrogen groups with isocyanate groups if they have more than oneactive hydrogen group. Where the multi-functional compound has only oneactive hydrogen group, the result is chain termination. Additional chainextenders having at least two active hydrogen groups may be added toincrease the chain length or to change the chemical characteristics ofthe polyurethane resin.

The polyurethane reaction is conducted under conditions well-known inthe art, typically below 100° C. in a protic solvent (e.g., aromatics,esters, ketones) in the presence of a tin catalyst. The resultingpolyurethane resin has a number average molecular weight of from 1000 to40,000.

In general, an excess of polyisocyanate is used so that an intermediatepolyurethane resin can be produced having free isocyanate groups at theterminal ends. The free isocyanate groups may then be capped with knowncapping agents for isocyanates.

Isocyanates useful in step (b) of the invention can be any of theisocyanates described above with regard to preparation of the compoundhaving a plurality of cyclic carbonate groups, individually or incombination.

It is often preferred to employ an aliphatic diisocyanate, since it hasbeen found that these can provide improved weatherability of thefinished coating. Examples include 1,6-hexamethylene diisocyanate,1,4-butylene diisocyanate, methylene bis (4-cyclohexyl isocyanate) andisophorone diisocyanate. Mixtures of diisocyanates can also be employed.

The proportions of the polyisocyanate, the reaction product of step (a),and any other active hydrogen-containing compounds may be chosen so asto provide an active hydrogen-terminated polyurethane resin or anisocyanate-terminated intermediate polyurethane resin. This can beaccomplished by utilizing a stoichiometric excess of active hydrogencompound or of polyisocyante.

If water-solubility is desired, it is important to buildwater-stabilizing groups into the polyurethane. Such groups can beanionic acid groups (e.g., carboxyl groups) or nonionic groups (e.g.,polyethers). For example, the presence of acid groups is capable ofrendering the composition water-dilutable when neutralized.

The acids that are employed to provide free acid groups in thepolyurethane resins of this invention are readily available. Theycontain at least one active hydrogen group and at least one carboxylicacid functionality. The active hydrogen group may be a thiol, a hydroxylor an amine, with primary amines being considered to have one activehydrogen group. Examples of such compounds include hydroxyl carboxylicacids, amino acids, thiol acids, aminothiol acids, alkanolamino acids,and hydroxythiol acids.

Compounds containing at least 2 hydroxyl groups and at least onecarboxylic acid are preferred. They can be prepared from an aldehydethat contains at least two hydrogens in the alpha position. Suchaldehydes are reacted in the presence of a base catalyst with twoequivalents of formaldehyde to form a 2,2-dihydroxymethyl aidehyde. Thealdehyde is then gently oxidized to the acid by known procedures. Theacids that are employed in the invention can be represented insimplification by Formula I: ##STR5## wherein R representshydroxymethyl, hydrogen, or alkyl of up to 20 carbon atoms andpreferably up to 8 carbon atoms.

Specific illustrative examples of such acids that are employed in theinvention include 2,2-di(hydroxymethyl) acetic acid,2,2,2-tri(hydroxymethyl) acetic acid, 2,2-di(hydroxymethyl) propionicacid, 2,2-di (hydroxymethyl) butyric acid, 2,2-di(hydroxymehtyl)pentanoic acid, and the like. The preferred acid is2,2-di(hydroxymethyl) propionic acid.

The polyethers that may be utilized to nonionically impartwater-solubility to the polymer are known in the art, and are described,for example, in U.S. Pat. No. 4,794,147, the disclosure of which isincorporated herein by reference. Useful polyether compounds arepreferably mono or difunctional polyethers with mono-functionalpolyethers being preferred. The functional groups on the polyethers maybe alcohol groups, thiols, amines, or mixtures of these functionalities.The monofunctional polyethers may be formed from monoalcohol-initiatedpolymerization of ethylene oxide, propylene oxide, and mixtures thereof.A polyether compound comprised of 100% ethylene oxide units isespecially preferred. When a polyether group is used as thewater-stabilizing group, it preferably comprises between 5 and 25% byweight of the final polyurethane resin and has a molecular weight offrom 1000 to 3000.

Longer-chain polyurethane resins can be obtained by chain extending thepolyurethane chain with a compound or mixture of compounds containing atleast two active hydrogen groups but having no carboxylic acid group,for example diols, dithiols, diamines, or compounds having a mixture ofhydroxyl, thiol, and amine groups, for example, alkanolamines,aminoalkyl mercaptans, and hydroxyalkyl mercaptans, among others. Forpurposes of this aspect of the invention both primary and secondaryamine groups are considered as having one active hydrogen.Alkanolamines, for example, ethanolamine or diethanolamine, arepreferably used as chain extenders, and most preferably, a diol is used.Examples of preferred diols which are used as polyurethane chainextenders include 1,6 hexanediol, cyclohexanedimethylol, and1,4-butanediol. While polyhydroxy compounds containing at least threehydroxyl groups may be used as chain extenders, the use of thesecompounds produces branched polyurethane resins. For purposes of thepresent invention, it is preferred to minimize the amount of branchingin the polyurethane resin. Therefore, if polyhydroxy compounds are used,they are preferably limited to a minor component of the polyurethaneproducing mixture. These higher functional polyhydroxy compoundsinclude, for example, trimethylolpropane, trimethylolethane,pentaerythritol, among other compounds.

The polyurethane resin may be chain extended in any manner usingmultifunctional compounds having at least two active hydrogen groups.Thus, these compounds may be added to the mixture of polyisocyanate,carbamate-containing polyol, and multi-functional compound, oralternatively, may react at an intermediate stage, to link two freeisocyanate groups that are present at the terminal ends of anintermediate polyurethane resin.

An intermediate polyurethane resin thus produced may be terminated withfree isocyanate groups. To accomplish this, an excess of thepolyisocyanate component is used. Of course, the molar ratio of theother components will be adjusted according to the desiredcharacteristics of the intermediate and final polyurethane resins. Thepolyol component should comprise no more than about 45% by weight of thereaction mixture and it is preferred that the polyol component comprisesfrom about 30% to about 40% by weight of reactants in the mixture.

In one preferred embodiment of the invention, a mono- ormulti-functional alcohol is used to terminate the reaction (cap the freeisocyanate groups) at the desired stage (determined by the viscosity andconcentration of isocyanate groups present). Particularly desirable forsuch purposes are aminoalcohols, such as ethanolamine, diethanolamineand the like, since the amino groups preferentially react with theisocyanate groups present. Multi-functional alcohols, such as ethyleneglycol, trimethylolpropane and hydroxyl-terminated polyesters, can alsobe employed in this manner. If a resin with only carbamate functionalityand no hydroxyl functionality, the intermediate polyurethane resin ispreferably capped with a mono functional alcohol or amine (e.g.,n-butanol).

The amount of polyisocyanate used in the mixture is preferably betweenabout 20% and 30% by weight of the reactants in the mixture, but willvary depending upon the presence and amounts of other polyols, thedesired acid number of the final polyurethane resin (if anionic waterstabilizing groups are used), and the desired molecular weight of thefinal polyurethane resin, as well as other factors known in the art. Theamount of polyisocyanate will also vary depending upon whether it isdesired to have the intermediate polyurethane terminated with freeisocyanate groups or with hydroxyl groups. Thus, where it is preferredto terminate the intermediate polyurethane resin with free isocyanatesfor capping with an alcohol, an excess of polyisocyanate may be used.Where the intermediate polyurethane resin is to be so capped, astoichiometric deficiency of polyisocyanate may be used.

When the polyurethane utilizes acid water-stabilizing groups, the amountof multi-functional component having at least one active hydrogen groupand at least one water-stabilizing group may vary depending upon thedesired acid number of the final polyurethane resin. The finalpolyurethane resin should have an acid number of at least about 10, andthe amount of this multi-functional component comprises between about 1%and about 25% by weight of the reactants of polyurethane producingreaction mixture (polyisocyanate, polyol, multifunctional compound, andoptionally other chain extenders, for example compounds having twoactive hydrogens but no carboxylic groups). It is preferable that theacid number be higher, because as the acid number increases, thewater-dispersibility of the polyurethane resin potentially increases. Ofcourse, the upper limit of the acid number will vary depending upon thechemical composition of the final polyurethane resin, but an acid numberof about 100 is, in general, the practical limit of polyurethane resinsof the present invention.

The amount of chain extender (including the reaction product of step (a)and other chain extending agents), when used to producing a polyurethaneresin, varies between about 2% and 25% by weight of the reactants. Theamount used will depend upon the amount of chain extension desired andthe desired molecular weight of the polyurethane molecule.

After the an anionically water-solubilized polyurethane resin issynthesized, a portion of the free carboxylic acid groups is neutralizedwith base to form salt groups. Preferably, the base is an aminocontaining compound. Tertiary amines are generally preferred overprimary and secondary amines because of the tendency of the primary andsecondary amines to react with aminoplast cross-linking agents.Preferred tertiary amines include tri-alkylamines, for example,trimethyl and triethylamine. Also preferred is triethanolamine.Particularly preferred is dimethylethanolamine.

The polyurethane resins of the present invention can be formulated,along with other components coating compositions which are sprayed orelectrostatically deposited onto metal or plastic substrates, forexample, automobile bodies. In general, a polyurethane resin formulatedas described herein, is mixed with a curing agent, a pigment grindresin, water and/or organic solvents, pigments including aluminum and/ormica particles and a rheology control agent. Other agents may beincluded, for example, various fillers, surfactants, plasticizers,stabilizers, wetting agents, dispersing agents, defoamers, adhesionpromoters and catalysts in minor amounts.

As indicated, a dispersion of the polyurethane resin is utilized as theprincipal or major vehicle resin. In general, the principal or majorvehicle resin comprises between about 20 and 80% by weight of the totalsolids present in the basecoat composition.

In a curable composition according to the invention, curing is effectedby a reaction of the carbamate-functional polyurethane component with acomponent (2) that is a compound having a plurality of functional groupsthat are reactive with the pendant carbamate groups on the polyurethane.Such reactive groups include active methylol or methylalkoxy groups onaminoplast crosslinking agents or on other compounds such asphenol/formaldehyde adducts, siloxane groups, and anhydride groups.Examples of curing agents include melamine formaldehyde resin (includingmonomeric or polymeric melamine resin and partially or fully alkylatedmelamine resin), urea resins (e.g., methylol ureas such as ureaformaldehyde resin, alkoxy ureas such as butylated urea formaldehyderesin), polyanhydrides (e.g., polysuccinic anhydride), and polysiloxanes(e.g., trimethoxy siloxane). Aminoplast resin such as melamineformaldehyde resin or urea formaldehyde resin are especially preferred.

A solvent may optionally be utilized in a curable composition used inthe practice of the present invention. Although the composition usedaccording to the present invention may be utilized, for example, in theform of substantially solid powder, or a dispersion, it is oftendesirable that the composition is in a substantially liquid state, whichcan be accomplished with the use of a solvent. This solvent should actas a solvent with respect to both the carbamate-functional polyurethaneas well as the curing agent. In general, depending on the solubilitycharacteristics of the components, the solvent can be any organicsolvent and/or water. In one preferred embodiment, the solvent is apolar organic solvent. More preferably, the solvent is a polar aliphaticsolvents or polar aromatic solvents. Still more preferably, the solventis a ketone, ester, acetate, aprotic amide, aprotic sulfoxide, oraprotic amine. Examples of useful solvents include methyl ethyl ketone,methyl isobutyl ketone, m-amyl acetate, ethylene glycol butylether-acetate, propylene glycol monomethyl ether acetate, xylene,N-methylpyrrolidone, or blends of aromatic hydrocarbons. In anotherpreferred embodiment, the solvent is water or a mixture of water withsmall amounts of co-solvents.

The curable composition used in the practice of the invention mayinclude a catalyst to enhance the cure reaction. For example, whenaminoplast compounds, especially monomeric melamines, are used, a strongacid catalyst may be utilized to enhance the cure reaction. Suchcatalysts are well-known in the art and include, for example,p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid,dodecylbenzenesulfonic acid, phenyl acid phosphate, monobutyl maleate,butyl phosphate, and hydroxy phosphate ester. Strong acid catalysts areoften blocked, e.g. with an amine. Other catalysts that may be useful inthe composition of the invention include Lewis acids, zinc salts, andtin salts.

In a preferred embodiment of the invention, the solvent is present inthe curable composition in an amount of from about 0.01 weight percentto about 99 weight percent, preferably from about 10 weight percent toabout 60 weight percent, and more preferably from about 30 weightpercent to about 50 weight percent.

Coating compositions can be coated on the article by any of a number oftechniques well-known in the art. These include, for example, spraycoating, dip coating, roll coating, curtain coating, and the like. Forautomotive body panels, spray coating is preferred.

Any additional agent used, for example, surfactants, fillers,stabilizers, wetting agents, dispersing agents, adhesion promoters, UVabsorbers, HALS, etc. may be incorporated into the coating composition.While the agents are well-known in the prior art, the amount used mustbe controlled to avoid adversely affecting the coating characteristics.

The curable composition according to the invention is preferablyutilized in a high-gloss coating and/or as the clearcoat of a compositecolor-plus-clear coating. High-gloss coatings as used herein arecoatings having a 20° gloss (ASTM D523-89) or a DOI (ASTM E430-91) of atleast 80. The curable composition according to the invention can also beused as the basecoat of a composite color-plus-clear coating.

When the coating composition of the invention is used as a high-glosspigmented paint coating, the pigment may be any organic or inorganiccompounds or colored materials, fillers, metallic or other inorganicflake materials such as mica or aluminum flake, and other materials ofkind that the art normally names as pigments. Pigments are usually usedin the composition in an amount of 1% to 100%, based on the total solidweight of components A and B (i.e., a P:B ratio of 0.1 to 1).

When the coating composition according to the invention is used as theclearcoat of a composite color-plus-clear coating, the pigmentedbasecoat composition may any of a number of types well-known in the art,and does not require explanation in detail herein. Polymers known in theart to be useful in basecoat compositions include acrylics, vinyls,polyurethanes, polycarbonates, polyesters, alkyds, and polysiloxanes.Preferred polymers include acrylics and polyurethanes. In one preferredembodiment of the invention, the basecoat composition also utilizes acarbamate-functional acrylic polymer. Basecoat polymers may bethermoplastic, but are are preferably crosslinkable and comprise one ormore type of cross-linkable functional groups. Such groups include, forexample, hydroxy, isocyanate, amine, epoxy, acrylate, vinyl, silane, andacetoacetate groups. These groups may be masked or blocked in such a wayso that they are unblocked and available for the cross-linking reactionunder the desired curing conditions, generally elevated temperatures.Useful cross-linkable functional groups include hydroxy, epoxy, acid,anhydride, silane, and acetoacetate groups. Preferred cross-linkablefunctional groups include hydroxy functional groups and amino functionalgroups.

Basecoat polymers may be self-cross-linkable, or may require a separatecross-linking agent that is reactive with the functional groups of thepolymer. When the polymer comprises hydroxy functional groups, forexample, the cross-linking agent may be aminoplast resin, isocyanate andblocked isocyanates (including isocyanurates), and acid or anhydridefunctional cross-linking agents.

The coating compositions described herein are preferably subjected toconditions so as to cure the coating layers. Although various methods ofcuring may be used, heatcuring is preferred. Generally, heat curing iseffected by exposing the coated article to elevated temperaturesprovided primarily by radiative heat sources. Curing temperatures willvary depending on the particular blocking groups used in thecross-linking agents, however they generally range between 93° C. and177° C. The compounds according to the present invention are reactiveeven at relatively low cure temperatures. Thus, in a preferredembodiment, the cure temperature is preferably between 115° C. and 150°C., and more preferably at temperatures between 115° C. and 138° C. fora blocked acid catalyzed system. For an unblocked acid catalyzed system,the cure temperature is preferably between 82° C. and 99° C. The curingtime will vary depending on the particular components used, and physicalparameters such as the thickness of the layers, however, typical curingtimes range from 15 to 60 minutes, and preferably 15-25 minutes forblocked acid catalyzed systems and 10-20 minutes for unblocked acidcatalyzed systems.

THE INVENTION IS FURTHER DESCRIBED IN THE FOLLOWING EXAMPLES. EXAMPLE 1

Preparation of polyol having at least one pendant carbamate group

A three neck round bottom flask was fitted with a coldfinger condenser,stirrer, ammonia inlet tube fitted with porous fritted glass tip andthermocouple. This apparatus was then placed in a metal container whichwas filled with dry ice, water, acetone and sodium chloride as a coldbath in order to control the temperature of the reaction. This reactorwas loaded with hydroxyalkyl cyclic carbonate (Glycar®) with an equalmolar amount of methanol. The temperature of the reaction components wasdropped to 15° C. at which time ammonia gas was bubbled through thereaction until the temperature of the reaction increased to 32° C. Atthis time the reaction was stirred and cooled back down to 15° C. Thisprocedure was continued until a carbonate peak was no longer seen in theinfrared spectrum. This should take approximately 12 hours depending onthe batch size and ammonia concentration.

After all the Glycar® was converted to the glycol carbamate the reactorapparatus was converted so that a heated vacuum strip can be performed.The vacuum strip was started at room temperature to prevent bumping orover expansion of the system. The temperature was slowly increased to80° C. under full vacuum 28 in Hg. The vacuum strip was complete whenthe gas chromatograph was clean of ammonia and methanol.

EXAMPLE 2

Preparation of solventborne polyurethane polymers with pendant carbamatefunctional groups

A three neck round bottom flask was fitted with a condenser, stirrer,nitrogen inlet tube and thermocouple. This reactor was loaded with thefollowing:

    ______________________________________    Ingredients           Weight    ______________________________________    Polyester polyol      2333.60    Methyl Propyl ketone  488.54    Neopentyl glycol      70.37    Carbamate glycol      141.95    Isophorone diisocyanate of (IPDI)                          816.75    Methyl ethyl ketone   192.62                          4043.83    ______________________________________

After all of the above ingredients were added the reaction mixture washeated to 210° F. As the reaction proceeds the reaction exotherms andthe reaction temperature rose to about 225° F. After the exotherm, thebatch temperature was held at 225°-230° F. for three hours where thefirst NCO number determination was taken. The target value was(0.26-0.28)meq NCO/gram resin. When the NCO number was in this rangethen addition of 143.15 grams of trimethylol propane (TMP) was added inthe capping stage of the reaction. After the addition of the TMP thereaction was held for 1.5 hours and a final NCO number determination wastaken. When the NCO number was determined to be nonexistent the reactionwas over and the reaction was cooled to 190° F. where 813.09 grams ofExxate® 800 was added.

EXAMPLE 3

Preparation of waterborne polyurethane polymers with pendant carbamatefunctional groups

A three neck round bottom flask was fitted with a condenser, stirrer,nitrogen inlet tube and thermocouple. This reactor was loaded with thefollowing:

    ______________________________________    Ingredients           weight    ______________________________________    Polyester polyol      1180.04    Neopentyl glycol      11.79    Carbamate glycol      35.58    Isophorone diisocyanate of (IPDI)                          413.01    Dimethylolpropionic acid                          61.41    Methyl ethyl ketone   97.40                          2046.28    ______________________________________

After all of the above ingredients were added the reaction mixture washeated to 210° F. As the reaction proceeds a slight exotherm occurs anthe temperature will rise to about 225° F. After the exotherm, thereaction temperature was held at (225-230)° F. for three hours where thefirst NCO number determination was taken. The target value was between(0.29-0.30) meq NCO/gram resin. When the NCO number was in this rangethen the addition of 82.96 grams of trimethylol propane (TMP) was addedin the capping stage of the reaction. After the addition of the TMP thereaction was held for 1.5 hours and a final NCO number determination wastaken. When the NCO number was determined to be nonexistent the reactionwas over an the reaction was cooled to 190° F. where 162 grams ofn-butanol was added. The reaction was further cooled to 180°°F. where162.67 grams of dimethylethanolamine (DMEA) was added and mixed for onehour to complete the salting phase of the reaction. After the hold, thetemperature of the reaction was lowered to 150° F. and 1667.41 grams ofdeionized (DI) water were charged to the vessel. After charging the DIwater, the reaction was mixed for two hours in order for completedispersion of the resin.

EXAMPLE 4

Preparation of solventhorne polyurethane polymers with pendant carbamatefunctional groups

A three neck round bottom flask was fitted with a condenser, stirrer,nitrogen inlet tube and thermocouple. This reactor was loaded with thefollowing:

    ______________________________________    Ingredients           Weight    ______________________________________    Polyester polyol      1732.49    Methyl propyl ketone  362.69    Neopentyl glycol      113.14    Carbamate glycol      59.11    Isophorone diisocyanate (IPDI)                          651.71    Methyl ethyl ketone   143.00    Dibutyltindilaurate   .05                          3063.65    ______________________________________

After all of the above ingredients were added to the reactor thereaction mixture was heated to 210° F. As the reaction proceeds a slightexotherm will be noticed an the reaction temperature will rise to about225° F. After the exotherm, the reaction temperature was held at(225-230)° F. for three hours where the first NCO number determinationwas taken. The target value was (0.24-0.25)meq NCO/gram resin. When theNCO number was in this range then the addition of 95.95 grams of TMP wasadded which was the capping stage of the reaction. After the addition ofthe TMP the reaction was held for 1.5 hours and a final NCO numberdetermination was taken. When the NCO number was determined to benonexistent the reaction was over an the reaction was cooled to 190° F.where 840.39 grams of Exxate® 800 was added and the reaction was over.

EXAMPLE 5

Preparation of solventborne polyurethane polymers with pendant carbamatefunctional groups with urea groups for dispersion properties

A three neck round bottom flask was fitted with a condenser, stirrer,nitrogen inlet tube and thermocouple. This reactor was loaded with thefollowing:

    ______________________________________    Ingredients           Weight    ______________________________________    Polyester polyol      1732.49    Methyl propyl ketone  362.69    Neopentyl glycol      113.14    Carbamate glycol      59.11    Isophorone diisocyanate IPDI                          651.71    Methylethyl ketone    143.00    Dibutyltin dilaurate  .05                          3063.65    ______________________________________

After all of the above ingredients were added the reaction mixture wasthen heated to 210° F. As the reaction proceeds a slight exotherm willbe noticed and the reaction temperature will rise to about 225° F. Afterthe exotherm, the batch was held at (225-230)° F. for three hours wherethe first NCO number determination was taken. The target value was(0.26-0.28)meq NCO/gram resin. When the NCO number was in this rangethen the reaction was cooled to 200° F. in order to get the reactionready for the capping stage. Addition of 74.95 grams diethanolamine(DEOA) was then added in the capping stage and the reaction was held forone hour. After the one hour hold a final NCO number determination wastaken. When the NCO number was determined to be nonexistent the reactionwas over an the reaction was cooled to 190° F. where 840.39 grams ofExxate® 800 was added after which the batch was cooled to roomtemperature.

EXAMPLE 6

A clear solventborne coating formulation was prepared by adding thefollowing ingredients in order under agitation. After all the componentswere added and mixed thoroughly, the paint was filtered into a containerfor later use.

    ______________________________________    Ingredients              Parts by Weight    ______________________________________    1.  Polyurethane resin with pendent                                 300.00        carbamate functionality (Example 1).    2.  Melamine crosslinker Resimene ® 747.                                 80.00        Note, other types of melamines can be        interchanged with the one chosen depending        on the application.    3.  Tinuvin ® 384B UVA light stabilizer.                                 7.50    4.  Tinuvin ® 123 N-alkoxy hindered amine                                 2.40    5.  Nacure ® 5225 amine-blocked acid catalysts                                 3.60    6.  Methylamyl ketone        11.40    7.  N-butyl alcohol/Normal butanol                                 75.00    8.  Exxate ® 800 high-boiling alkyl acetates of                                 100.00        primary alcohols.    ______________________________________

EXAMPLE 7

A white waterborne basecoat coating formulation was prepared by addingthe following ingredients in order under agitation. After all thecomponents were added and mixed thoroughly, the paint was filtered intoa container for later use.

    ______________________________________    Ingredients              Parts by weight    ______________________________________    1.  Clay rheology agent 3.0% in water                                 12.88    2.  Melamine x-linker Resimene ® x-747                                 5.80    3.  Solvent Dowanol ® DPM                                 1.45    4.  Polyurethane resin (Example 3) with                                 26.43        pendent carbamate functionality.    5.  Fumed silica rheology agent                                 6.84    6.  White pigment paste      44.03    7.  Tinuvin ® 1130       0.33    8.  Nacure ® 2500 amine-blocked acid catalysts                                 1.80    9.  Dimethyl ethanol amine 20% solution in                                 0.44        DI water to adjust pH of system.                                 100.00    ______________________________________

EXAMPLE 8

A white solventborne basecoat formulation was prepared by adding thefollowing ingredients in order under agitation. After all the componentswere added and mixed thoroughly, the paint was filtered into a containerfor later use.

    ______________________________________    Ingredients              Parts by weight    ______________________________________    1.  Melamine ® x-linker Cymel ® 327                                 12.00    2.  Melamine ® x-linker Cymel ® 1158                                 4.56    3.  Solvent Exxate ® 1000                                 4.78    4.  Microgel rheology control agent                                 16.45    5.  Polyurethane polymer with pendent                                 10.73        carbamate functional groups (see        example 4).    6.  Flexible high solids acrylic hydroxyl                                 6.32        functionality.    7.  Flow additive Coroc ® A-620-A2                                 0.16    8.  Solvent Xylene           0.15    9.  Tinuvin ® 1130       1.08    10. White pigment paste      37.49    11. N-butyl acetate          4.15    ______________________________________

The coating compositions of Examples 6-8 were sprayed onto test panelsand cured by baking to form hard cured coatings.

The invention has been described in detail with reference to preferredembodiments thereof. It should be understood, however, that variationsand modifications can be made within the spirit and scope of theinvention.

What is claimed is:
 1. A method of preparing a polyurethane havingpendant carbamate groups, comprising the steps of:(a) reacting acompound comprising a plurality of cyclic carbonate groups with ammonia,ammonium hydroxide, or a primary amine to ring open the cyclic carbonategroup to form a polyol having a plurality of pendant carbamate groups,and (b) reacting a mixture comprising said polyol having a plurality ofcarbamate groups and a polyisocyanate to form a polyurethane havingpendant carbamate groups.
 2. A method according to claim 1, furthercomprising the step of capping the polyurethane from (b) with an activehydrogen-containing capping agent.
 3. A method according to claim 1wherein the compound having a plurality of cyclic carbonate groups isprepared by reacting a hydroxyalkyl cyclic carbonate with apolyisocyanate or a polyanhydride.
 4. A method according to claim 1wherein the compound having a plurality of cyclic carbonate groups isprepared by reacting a polyepoxide with CO₂.
 5. A method according toclaim 1 wherein the compound having a plurality cyclic carbonate groupsis reacted with ammonia or ammonium hydroxide.
 6. A method according toclaim 1 wherein the mixture in step (b) further comprises at least oneadditional compound having a plurality of active hydrogen groups.
 7. Amethod according to claim 6 wherein the active hydrogen compound is apolyester polyol.
 8. A method according to claim 6 wherein the activehydrogen compound is a dihydric alcohol having a carboxyl group appendedthereto.
 9. A method according to claim 1 wherein the mixture in step(b) further comprises a polyester polyol and a dihydric alcohol having acarboxyl group appended thereto.
 10. A method according to claim 1,wherein the compound comprising a plurality of cyclic carbonate groupsis monomeric.
 11. A method according to claim 4, wherein the polyepoxideis an oligomeric or polymeric polyepoxide.
 12. A method according toclaim 1, wherein the polyol is oligomeric or polymeric.
 13. A methodaccording to claim 1, wherein the polyol is an oligomer or polymerselected from the group consisting of acrylic polymers, acrylicoligomers, epoxy polymers, and epoxy oligomers.